The interaction of medications with their storage vessels and delivery devices is attracting increasing attention. Such vessels and devices include glass vials (e.g., with rubber septa), glass or plastic syringes (e.g., with rubber-tipped plunger seals), and plastic metered-dose inhalers. For example, understanding the propensity of macromolecular protein-based pharmaceuticals to adsorb to storage vessel walls is of critical importance. If the adsorption rate is much greater than the desorption rate, the actual dosage of medication delivered to patients may be significantly lower than what was intended. In addition, it is often assumed that materials used for pharmaceutical storage are inert, i.e., unreactive and unchanging over the course of their service life. However, constituent chemical elements of these vessels (e.g., ions, solvents, surfactants, unreacted species) are known to leach out into liquid drug solutions and suspensions. The leachate itself may be harmful to the patient if administered with the drug. In addition, the leachate may perturb the pH, salinity, turbidity, etc. of the liquid drug. Such perturbations may have a dramatic impact on the biochemical activity of the drug (e.g., by changing the structure of pharmaceutical proteins), reducing the drug's efficacy or rendering it harmful.
Some medical articles are deliberately treated with lubricating surface coatings to improve their performance. For example, disposable, graduated syringe barrels may be siliconized to improve their lubricity. The sealing member attached to the drug-contacting syringe plunger tip may be surface-treated in the same way. Such lubrication facilitates sliding of the sealing member over the barrel's surface. This helps to ensure smooth delivery of the liquid drug stored in the syringe when the plunger is depressed. In addition to improving the convenience of using these syringes, lubrication prevents accidental administration of drug overdoses. A first surface which has been in contact with a second surface for a period of time must overcome stiction (static friction) in order to begin sliding over that second surface. Stiction between two surfaces is reportedly exacerbated by cold storage (as in a refrigerator). Syringe plungers and barrels are no exception. In order to start the plunger's sliding motion and push out the drug, one must initially apply more force than is later required to keep the plunger in motion. It may be difficult for medical personnel to determine exactly when different amounts of force are required during drug administration. Hence, the plunger may be pushed past its intended stopping point along the syringe barrel's graduations, resulting in an overdose. Lubricating coatings are intended to reduce both stiction and the expected dynamic friction once the sealing member is in motion.
Siliconization is a popular lubrication approach. That is, a small amount of liquid silicone oil (e.g., a low-molecular-weight polydimethylsiloxane) may be added to the syringe barrel surface or the sealing member surface, or both. Silicone oils have the advantages of chemical stability (being resistant to thermal and oxidative insult) and wide commercial availability, and the reputation for bio-inertness. For example, liquid silicones have been used extensively for anatomical enhancements, such as breast implants.
However, recent studies have cast doubt on some silicones' inertness. For example, silicone lubricants have been reported as encouraging the aggregation of proteins in solution, even at very low silicone concentrations. Insulin solutions have been reported to go increasingly turbid with prolonged exposure to silicone-lubricated syringes—a hallmark of macromolecular aggregation. These effects have disadvantages. The relationship between drugs and storage/administration devices preferably remains purely physical en route to the patient. Drug formulators generally want the confidence that their medications can be readily administered at the intended dosages, whether in dry powder, aerosol, or liquid form. Hence, there is a critical need for medical articles that preserve drug efficacy and safety during storage and administration.